Gamma-Polyglutamic Acid Reduces Heavy Metal Uptake and Stabilize Microbial Biosafety in Edible Mushroom Cultures

This study evaluated the influence of gamma-polyglutamic acid (γ-PGA) on the heavy metal sorption efficiency of three edible mushroom species—Pleurotus ostreatus, Agaricus bisporus, and Boletus edulis—exposed to cadmium (Cd), lead (Pb), and their mixtures (in a 1:1 ratio). The experiment presented an innovative approach—combining the natural sorption properties of mushrooms with the addition of γ-PGA, which has strong chelating properties. Sorption assays were performed using escalating γ-PGA concentrations (1, 2, and 5 mL to 250 mL of liquid medium), with data analyzed via generalized linear models employing a gamma distribution and a log link function. Results revealed that sorption efficiency was highest at the lowest γ-PGA concentration and decreased significantly with increasing γ-PGA levels across all species and metal treatments. Notably, P. ostreatus and A. bisporus demonstrated superior and more stable sorption capacities relative to B. edulis, which exhibited greater variability. These findings suggest that while edible mushrooms are effective biosorbents for heavy metals, higher γ-PGA concentrations may inhibit metal uptake by chelating metals in solution and reducing their bioavailability. Additionally, γ-PGA at 1 mM markedly enhanced antimicrobial activity against Salmonella enteritidis and Escherichia coli (with a 20% increase in growth inhibition zone compared to the control group) in mushroom cultures and when applied independently. This dual functionality underscores the potential of γ-PGA–mushroom systems for bioremediation and food safety applications, highlighting the need for the careful optimization of γ-PGA concentration to maximize biosorption efficacy and antimicrobial benefits.